Adhesives and method of making same



Patented Oct. 9, 1945 ADHESIVES AND METHOD OF MAKING SAME Thomas RaymondGriffith,

Ottawa, Ontario,

Canada, assignor to The Honorary Advisory Council for Scientific andIndustrial Research, Ottawa, Ontario, Canada, a corporation of Canada NoDrawing. Application August 23, 1940, Serial No. 353,914

15 Claims This invention relates to rubber derivatives and to a methodfor preparing the same. It particularly relates to an improved adhesivefor adhering rubber to metal.

Rubber conversion products, such as rubber derivatives having lessunsaturation than rubber when it contains an equivalent quantity ofcombined added elements, have been prepared for adhering rubber to metaland for a base for coating compositions and the like. Generally, thesederivatives have proven unsatisfactory for bonding rubber to metalbecause they are so thermoplastic (becoming more plastic than cruderubber at elevated temperatures) that the mold must be cooled before thecomposite article of rubber and. metal is removed. Also, thebonded'articles produced with these derivatives had relatively littlestrength at temperatures such as 100 C.

In my'prior applications, United States Serial No. 277,086, filed June2, 1939, and United States Serial Nos. 292,699 and 292,700, filed August1939, of which this application is a continuation in part, I havedescribed rubber derivatives, and methods for preparing the same, havingsubstantially non-thermoplastic properties, being less plastic thancrude rubber at elevated temperatures. Composite articles united by suchrubber derivatives may be readily removed from a hot mold withoutdeleterious eftects, but the hot strength of such articles is still muchless than their cold strength.

It is, therefore, an important object of this invention to provide amethod for improving the hot strength of rubber derivatives having lesschemical unsaturation than the rubber.

While a single coat of solutions of the derivatives described in theabove applications may be used for adhering rubber to metal, the bondproduced is usually improved considerably when two or more coats ofadhesives having decreasing hardness are successively applied to themetal before the rubber is vulcanized thereon.

It is another object of this invention to provide a solution of a rubberderivative which forms a strong bond when a single coat is suitablydisposed between the rubber and the metal.

It is another object of this invention to provide a rubber derivativehaving improved properties, both when used as an adhesive and as a basefor paints.

It is a further object of this invention to provide a rubber derivativewhich adheres rubber to metal with greater strength at both normal andelevated temperatures.

It is a still further object of this invention to provide a method forpreparing rubber derivatives and solutions thereof having superiorproperties for bonding rubber to metal.

These and other objects, which will be apparent from the followingdescription of the invention, are accomplished by incorporatingvulcanizing agents, particularly sulphur, and/ or a rubber vulcanizationaccelerator, into a rubber derivative which may be prepared by any ofthe various methods whereby one obtains a rubber derivative having lessunsaturation than rubber when it contains an equivalentamount of anysame as natural rubber, namely (C5H8):c.

added, elements combined with the carbon and hydrogen. These derivativeshave carbon and hydrogen in the same ratio as in the rubber, and thehydrocarbon portion of the empirical formula of the mostdesirablederivatives is the They may also have limited amounts of addedelements combined with the carbon and hydrogen, or otherwise present,however.

The characteristics of the rubber derivative used as the base product inthis invention for the preparation of adhesives and paints are, however,important and the stronger bonds are obtained when the lessthermoplastic rubber derivatives are used. The most desirable rubberderivatives are prepared by incorporating into solid rubber, as bymilling, conversion reagents which are adapted to convert rubber into anisomer of rubber or an isomer of rubber addition'products having lesschemical unsaturation than rubber or normal rubber addition products ofthe same composition, and which are usually either of an acidiccharacter or are a mixture 'of ingredients which may combine to produceacidic materials; forming the mixture into thin sheets or into anotherform, such as rods, having a thin section; heating the sheets undersuitably controlled conditions until the desired reaction occurs; andmasticating the product to solubilize it.

The properties of the rubber derivative depend to a large extent on thereagent used in its formation. Certain of the reagents, however, giveproducts that are more desirable than products produced with otherreagents. Conversion reagents which, in general, have been found. togive products with good properties may be mixtures of one or more saltsof a strong acid in conjunction with a weakly acidic substance, with orwithout sulphur and selenium. It is thought that these conversionreagents have a polymerizing action on rubber under proper condi- P205or PC'ls, which with water forms ,a weak acid. Aluminunr acid sulfate,whenlproperly' used with a cooperating material of thecharacter ofphosphoric acid, produces rubber reaction products having exceptionallydesirable preperties.

Examples of the acid sulfates or double sulfates which are particularlydesirable for use are those of aluminum, iron (both --ferric andferrous) the alkali meta-ls, including ammonia, alkaline earthmetals-and the closely related alums, potassium alum and other alums. Inaddition to'the acid sulfates, certain sulfates may .be usedadvantageously.- Examples of these are sulfates of iron (both ferric andferrous) aluminum, copper, mercury and cadmium. Examples of salts ofstrong acids other than sulphuric acid are bromides of mercury and zinc,chlorides of mercury, tin and -aluminu-m, and alkali metal iodides.Phosphor-"lo acid is a-very good example .of a weakly acidic substancedesirable for use in forming'the rubber conversion product hereinbeforementioned. For some uses, where it is desirable to have the conversionproduct somewhat more soluble in rubber solvents, oxalic acid has beenusedadvant ageously. Gt-her weak acids that are Preferably, there shouldbe present in the mix from 1.5% to 15% of water, including any water ofcrystallization that may be present. The amount of water may varyoutside pfand beyond these limits for the production of materials withdesired specific properties, but usually in the pro- .duction ofadhesives, 3% to about 9% or 10% of water should be present in the mix.Ordinarily, some free water is added during the mix- .ing to bring thetotal quantity within this value.

Since water may be milled into the rubber more rapidly than liquid acidsand the water and solid anhydrideof a weak acid produce less deleteriouseffects en the rubber than liquid acids, it will also desirable foruseare :benzoic, tartaric,

p-ht-halic and salicylic. The particular acid may be selected for theproperties it gives to the conversion product, as various acids seem toimpart slightly "different properties.

These weakly acidic materials, while assisting inthe formation ofthe-rubber derivatives, are not absolutely essential ingredients of theconversion reagents, and may in some cases be omitted.- The quantity ofsalts of strong acids required to convert the rubber into the derivativeis, however; much larger when the weakly acidic compound is omitted as apart of the conversion reagent. Thus, the rubber derivative may beprepared by usingaluminum sulfate alone as the conversion reagent, "butits properties as an adhesive are improved and the quantity of reagentsrequired is decreased when phosphoric acid or other weak acid is alsopresent.

the preparation of the conversion products, the cpnversionf reagent ismilled or otherwise suitably mixed with the rubber until it isthoroughly incorporated. It has been found that the amount and theconditions of mastication also haye an influence on the character of theconversion product produced. Products having less plasticity and greaterstrength are produced with given reagents when the amount ,ofmastication is'reduced to a minimum. .Mastication in the presence of aliquid acid,'su,chas sulfuric, sulfuro. .S, Sulfonic, et'c., isparticularly harmful. .Conyersion reagents of a solid nature are,therefore, preferred both because they may be quickly incplporated'withaminimum of milling and the r'nastication of the rubber in the presenceof such ingredients is less harmful to the character .of

the conversion product.

be seen that it is advantageous to utilize a solid acid anhydride andwater instead of liquid acids. 'Phesphoric acid is an example of theacid constituent of the reagent preferably used, and it isdesira le tomix its solid anhydride (P205) into the rubber and then add any waterdesired.

,The mixed product is preferably formed into relatively thin sheets orin a form of relatively thin section; the sheets usually have athickness of about 3 or 4; mm., or so, and are placed in an oven withtemperature control and heated for an appropriate period. Thetemperature and time of heating greatly affect the character of thereaction product. During the heating an exother- Inal reaction occursand if the temperature of the sl ieets rises too high, the adhesivequality of the product will be weaker at elevated temperatures. Thetemperature in the sheets should not rise substantially higher thanabout 170 C, and superior products are obtained whenthe temperatureremains considerably below this value. Preferably, the oven temperatureshould not be higher than about 1&0 C. to 115:5- C. The control oftemperature is aided by the use of thin sheets having a thickness ofabout 2 or '3 mm., or even less. Also, the evaporation of the watercontained in the sheets serves to keep'the temperahim down. "If desired,an inert gas .or'air may be 'c'irculatd over the sheeted material in theoven.

It is preferred, however, to heat the mix in an at o ph e havin less oxyen p ssu h the partial pressure of oxygen in air, such as is obtainedwith an inert gas or in a vacuum. Ordin ily, a re ativ ly high vacuum,uc a abo 500 mm., or more, of mercury is preferred. By earrying' out thereaction in a Vacuum, the tendency for portions of the thin sheets tobecome harder than others is substantially eliminated, and a moreuniform product is obtained.

The formation of the m x into t in sections, Such as h ets 1 mmto about7 or 8 mm., or me r b y 2 t 3 mm, o so. is n f cia ga ss of theconversionreagent used, and is 2.180111}- p rtant in facilitat n th eacon t eing ound tha the rea tion t kes pl e with d fi cu'l y whenrelatively thick sections are used.

y t u o ery th n sheet-s, su h as i or so in thickness, it is" possibleto carry on the reaction at temperatures as low as C. to 0., and aderiyative having higher molecular w i ht is pr duced which s relat velyless s lu and l v ly more elast c at e a d mpe atures; The use ofconversion reagents which are s l d or volat li e with difficulty s dvanag u in carrying out the reaction when the material is in the form ofthin sheets. When. readily volatile reagents are ,used and the mix issheeted nto thin sheet siifii ient of the ea nt or a ent may be v latliz d that th r a t on i incomplete, even in the middle of the sheet. 7

The sheeted material is heated for a suflicient time to allow thereaction to progress to the desired stage. A somewhat harder product isproduced by increasing the quantity of conversion reagent, by heating agiven mixture for a longer period of time at the same temperature, or byreducing the thickness of the sheets. The reaction takes place at lowertemperatures when larger quantities of the conversion reagent are usedor when the mix is sheeted to relatively thinner sheets. The reactionproducts produced at the lower temperature, however, are relatively lesssoluble on milling, particularly when the product is relatively soft.

After the reaction, the material is substantially insoluble in rubbersolvents, but solubility may be restored by masticating the material fora sufiicient time on a rubber mill or in a suitable mixer.

Solubility of the product depends to a large extent on the amount ofmastication, and for the production of adhesives such as are desired forbonding rubber to metal, the mastication of the reaction product ispreferably reduced to the minimum required for solubility. Working ormastication of the reaction product has a more harmful effect on thestrength of the adhesive when acids are present and it is, therefore,preferable to incorporate a basic material into the product as soon aspossible during this mastication period to neutralize any acids oracidic substance that might be present or formed during the reaction. Inthe making of a conversion product for use as an adhesive, an alkali,such as NaOI-I, may be used if desired, and the soluble salts removedwith water, but it is usually preferable to add basic materials, such asoxides or carbonates of zinc, magnesium, etc., which neutralize acidsand which may be left in the masticated product.

When the conversion product is to be used for the making of adhesives,powdered solids, such as zinc oxide, or finely divided, fibrousmaterials, such as short fiber asbestos, may be added to the conversionproduct as it is being reworked or remasticated. These materials appearto have the effect of improving the strength of the bond when thesolution of the conversion product is used as an adhesive for bondingrubber to metal, etc.

When the conversion product is to be used in the manufacture of paintsand the like, the product may or may not be neutralized. A somewhatincreased solubility is obtained when residual acidic substances or acidpigments are present.

The quantity of conversion reagent used in forming the rubber conversionproduct is dependent on the character of the conversion product desiredand the conversion reagent used. Larger quantities of conversionreagent, such as aluminum acid sulfate with phosphoric acid, give harderproducts when heated for a given length of time. When a weakly acidiccompound is not present, a larger quantity of the acid salt of strongacid must be used to produce conversion products of the same hardness.This may amount to or more of the rubber mixture.

'When a weak acid, such as phosphoric, is also present, the total ofboth ingredients of the conversion reagent may in some cases be lessthan 10% of the rubber mixture.

The characteristics of the derivatives produced are also somewhatdependent on the rubber used as a starting material, and the strongestadhesive is produced from rubber, such as pale crepe, smoked sheet, etc.Masticated rubber may, how.-

ever, be used as a basis for preparation of the derivative, but it isdesirable that the amount of mastication be kept at a minimum for themaking of adhesives. Other rubberlike materials, such as reclaim rubberand African or Congo rubber, may be used for the production of rubberderivatives of the type herein disclosed.

It has now been found that when sulphur is incorporated in the rubberderivatives having less unsaturation than the rubber used in itspreparation, such for example as are described above, the properties aregreatly changed so that improved adhesives and paints are obtained.

The method of incorporating the sulphur, the

presence of accelerators, the type of accelerators,

the presence of additional vulcanizing .agents, as well as the initialcharacteristics of the rubber derivative, affect the characteristics ofthe adhesive or paint produced.

' 'In the preparation of an adhesive highly desirable for use as asingle-coat adhesive, the rubber derivative is prepared as above setforth, dissolved in a rubber solvent, such as gasoline, and asubstantial quantity of one or more rub- -ber vulcanizing agents, suchas sulphur or selenium, is mixed into the solution thus prepared. Anaccelerator should also be present in the mix to insure combination ofthe sulphur with the rubber derivative when the latter is heated duringthe preparation of composite articles having rubber vulcanized to alayer of adhesive applied on the metal.

While some of the sulphur added in this manner apparently combines withthe rubber derivative while it is in solution, as is evidenced by thefact that the adhesive solution usually becomes more stringy, a majorportion is present as suspended, free. sulphur. When one or more coatsof the adhesive are applied to metal and rubber vulcanized in contacttherewith, free sulphur in the adhesive chemically combines with therubber derivative, rendering it much less plastic and stronger atelevated temperatures, thus increasing the strength of the bondedarticle. Some of the free sulphur may migrate into the adjacent rubberduring the vulcanization thereof, and thus produce a gradient havingdecreasing hardness from the surface of the rubber in contact with theadhesive.

More than 5% of the sulphur or equivalent vul- I canizing agentsincorporated in the adhesive in this manner noticeably improves thestrength of the bonded article, particularly at elevated temperatures,but less than 5% of sulphur added in this manner does not improve thebonding strength. The quantity of sulphur preferably added is 15% or 20%by weight, based on the rubber derivative. Even more than 20% of sulphurmay be present in the adhesive without greatly decreasing the strengthof the bond, but it is pref erable to maintain the percentage below 50%of sulphur.

The accelerator may be incorporated into the rubber conversion reagentmix prior to the reaction which forms a derivative having less chemicalunsaturation than rubber, but it is preferable that it be incorporatedin the derivative during the mastication or solubilization period.'However it may also be added to the solution of the derivative. Whilerubber vulcanization accelerators in general are useful in theadhesives, the selection of the accelerator is very important inobtaining high bonding strength. Those having one or more primary aminogroups, and particularly those having a plurality of amino groups, suchfor example as 2,4 diamino diphenylami'ne, or any accelerator whichexerts a stiffening or antiplasticizingefiec't on solid rubber mixes,are much preferred. When an accelerator and/or an anti-oxidant such asmeta-toluylenediamine or a member of .the.Neozone series, which producesstiffening'action is used, the strength of the bond produced by theadhesive is greatly increased and theifullest benefits of this inventionare obtainable, whereas when the usual accelerators which exert aplasticizing action on the mix are :used, the strength of the bondobtainable between rubber. and metal .is much less at elevatedtemperatures.

,When relatively large amounts of sulphur, such as or ormore, areincorporated into the adhesive, it has been found that most of thisamount must be added to th'erubberderivative after it has beendissolved, for when a considerable amount of sulphur is masticated: ormilled into the rubber derivative, sufilcient'oithe sulphur combinestherewith to prevent. the mixture from becoming soluble in petroleumsolvents, even after continued milling. It has been found, however, thatrubber derivatives having less unsaturation than a'rubber with equalquantites of combined elements may contain as much as about 3% ofcombined sulphur, and while the unworked product is insoluble, it may besolubilized by milling or by suitable mastication. Even 3% of sulphur,ali of which may be chemically combined with the adhesive base, improvesthe heat resistance of the bonds produced, and such a resinous materialwith combined sulphur has a lighter color and improved aging properties;It isparticularly desirable as a base for paints.

If more than 3% of chemically combined sulphur is present in the aboverubber derivative, or if difficulty is experienced in rendering itsolubleby mastication, it has been found that solubility may be readilyimparted thereby by masticating the insoluble or difiicultly solublerubber derivative either with a suitable quantity of an easily solublerubber derivative, for example, sufiicient of a derivative containingless than 3% of sulphur to bring the sulphur content below about 3% ofthe total, or with rosin or other readily soluble resinous materials.

Additional sulphur or selenium may also be added to solutions of thederivatives containing combined sulphur to further improve its bondingstrength so that an exceptionally desirable adhesive for adhering rubberto metal is produced.

In the preparation of the soluble derivative containing combinedsulphur, the sulphur, with or without an accelerator, may beincorporated by mastication either before or after the heating step, butif incorporated'after the reaction the product should be again heated toinsure combination of the sulphur, particularly when the rubberderivative is to be used'as a paint base.

It is desirablefto have some selenium present, as it appears to act asan antioxidant, so that the material has improved aging properties. Theselenium maybe incorporated by mastication in the mix before theexothermic reaction, or it may be incorporated later. When it isincorporated on the mill, or before the exothermic reaction takes place,it acts to increase the solubility and plasticity of the product. i f

The solubilizing eiiect of selenium is so marked that the amount ofcombined sulphur may be increased above 3% when selenium is present inthe rubber derivative. Because of the plasticizing eifect, however, itis undesirable that the amount of selenium added. in this manner beexcessive.

The quantity of seleniiun which is present during the formation of thederivative should be such thatthe desired solubility is obtained withoutincreasing. the plasticity to an undesirable extent.

to the solution. Its presencauncombined with the derivative, seems toimprove the strength of the bond when the derivative is used as anadhesive. Theuncombined selenium added in this manner may be present inlarger percentages than those desirable during the reaction forming therubber derivative. Thus,.'5% or 15% or so selenium may be used in theadhesive solution, with orlwithout sulphur, which may also be present inamounts up to 15% to 25%, or 30% or so, if desired.

The harness and plasticity of the soluble but undissolved derivative ofrubber are also important in producing an adhesive having thehighestbonding strength. In fact when the hardness and plasticity areheld within rather definite limits, it has been found that a single coatof the adhesive will produce a strong bond even though sulphur beomitted entirely.

For a single coat adhesive, particularly when free sulphur is absent,the most desirable range of hardness and plasticity of desirablederivatives, having less unsaturation than rubber which contains anequivalent amount of added elements chemically combined therewith, canreadily be determined by hand tests. The hardest derivative, which isstill suitable when free sulphur, etc. is absent, is just brittle atroom temperature (23 (3.), that is. if the temperature israised a fewdegrees, say 10 degrees, the material may be slowly bent in the hand inpieces, say one inch long and one-fourth inch thick. The soi testmaterial that may be used as a'single coat is quite flexible and rubberyat room temperature.

Although better results are obtained when the quantity of conversionreagents is chosen so as to produce a solubilizable derivative withoutor with combined sulphur or selenium, or both, having a plasticitywithin the range above specified, good results are obtained withadhesives made from derivatives having hardness and plasticity outsideof the range stated when free sulphur is present in substantialproportions.

The following examples, in which parts are by weight, illustrate thepreparation of rubber derivatives and adhesives embodying thisinvention:

Example 1 Parts Rubber (pale crepe or equivalent) 500 Aluminum acidsulfate 44 Phosphorus pentoxide 11 Water l0 Selenium 1 Sulphur 2.5

The above ingredient were suitably mixed on a rubber mill and themixture formed in a shape saturation than rubber when 'it contains equalquantities of combined sulphur and selenium or equivalent quantities ofother elements, was produced. The specific empirical formula of thisderivative is (CH8)xSySez, where x, y and z are numerical values.

Example 3 The derivatives prepared in Examples 1 and 2, both of whichhave the desired properties for an adhesive base, were separatelymasticated on a rubber mill to render them soluble. During thismastication or solubilizing period, they were sep arately compounded inaccordance with the following proportions;

. Parts Above rubber derivatives 100 Magnesium oxide Antioxidant(phenyl-beta-naphthylamine) 2 Carbon black 40 These soluble, compoundedderivatives, which have hardnesses and plasticities within the abovedescribed optimum range, were separately dissolved in suitablequantities of rubber solvents to produce cements having the desiredviscosity.

Composite articles of rubber and metal were prepared from both of theabove cements by applying a single coat of the cement to a clean surface,(preferably sand blasted) of the metal, allowing it to dry, andvulcanizing suitably compounded rubber thereon. When tested at roomtemperature, the bond between the rubber and the metal was around 600lbs/sq. in. when either solution was used. However, the strength of thebond using the derivative prepared in Example 1 was somewhat better thanthat from the derivative of Example 2. When tested at 100 0., the bondsproduced by the above cement containing the combined sulphur werestronger than those produced by the other cement. The strength of thebonds at the higher temperature was around 300 lbs/sq. in. 7

Example 4 r The derivatives prepared in Examples 1 and 2 were separatelymasticated on a rubber mill to render them soluble. During thismastication or solubilizing period, they were separately compounded inaccordance with the following pro.

These derivatives, which have hardnesses and plasticities' within theabove described optimum range were, after compounding as above,separately dissolved in suitable quantities of rubber solvents toproduce cements having the desired viscosity.

Fifteen parts of finely ground sulphur, 80% or of which passed through a325 mesh screen, were incorporated by stirring in each of the cs ments.These cements thus prepared, when used as above to produce compositearticles of rubber and metal or of rubber and a rigid material, producedbonds between the rubber and metal of such strength that the rubber torein itself when the articles were tested at both elevated and normaltemperatures. 7

- Example 5 When 5 or 10 parts of finely ground selenium (based on thesolid rubber derivative) were added by stirring to either of the cementsprepared in Example 4, a single-coat adhesive forming an excellent bondbetween rubber and metal, but a weak bond between chloroprene (neoprene)and metal, Was produced. However, if either of the cements of Example 4contained 20% to 40% of a less volatile solvent such as kerosene, or aplasticizer such as light mineral oil, and about 5% selenium togetherwith sulphur was added and stirred therein, the adhesive formed bondshaving strengths of 850 lbs/sq. in. and 1200lbs./sq. in, respectively,between neoprene and metal, and between rubber and metal. Thepercentages given are based on the rubber derivative.

Example 6 Particularly desirable compositions for adhering neoprene tometal are prepared in accordance with the following formulae:

The proportions of the ingredients in the above examples may, as pointedout above, be varied to produce rubber derivatives of varying degrees ofhardness. In the preparation of composite articles, a plurality of coatsof adhesive having the same or'difierent hardnesses may be used ifdesired. Also, a rubber cement'or tie cement containing part rubber andpart rubber derivatives may be superimposed over the adhesive on themetal. I r

When the derivative of Example 1 is to be used as a paint base, it ispreferred to increase the quantity of conversion'reagents' and seleniumso that a harder and more readily soluble product than that of Example 1is produced.

, Although the aluminum acid sulfate and the phosphorus pentoxide'havebeen set out in definite proportions in Examples 1 and 2 above, it is tobe understood that such proportions have been given as illustrative ofthe invention, and the proportions may be varied considerably to produceuseful exothermal reaction products. Other reagents, such as thosementioned herein which also' effect exothermal reactions in a thinlysheeted rubber mix to form such reaction products, may be substitutedfor those specifically mentioned in the examples. Also, the specificamotmts of compounding ingredients mentioned in the examples areunderstood to be illustrative and not to indicate critical values orthose necessary for employment of these ingredients.

While pale crepe rubber, or the equivalent, has been specified inExamplesl and 2, and such rubber is usually preferred it is to beunderstood that other types of rubber may be substituted therefor. Suchother types of rubber may comprise. reclaim rubber or rubberlikematerials, such as synthetic rubbers having an unsaturated structuresimilar in nature to rubber, and which will undergo a polymerizing orcyclizing reaction to produce a solubilized product having lessunsaturation than the raw material when it contains an equivalent amountof added elements chemically combined therewith.

By far the strongest and most heat resistant bonds between rubber andmetal are produced when derivatives are prepared, in the manner setforth above, by incorporating the above conversion reagents into solidrubber and heating the rubber mix in a form having thin section. It hasbeen found, however, that the strength and heat resistance of bonds,produced from rubber derivatives in general which fulfil thequalification of having less unsaturation than rubber when it containsan equivalent percentage of combined added elements, are increased bythe addition of vulcanizing agents, such as sulphur, to their solutionsor dispersions in accordance with this invention. Thus the bondingstrength and heat resistance of the thermoplastic rubber derivativesdescribed in Fisher Patent 1,605,180, as well as the chlorine-containingpolymerized derivative of rubber set forth in the Brunson Patent1,797,188, are improved when sulphur and accelerators are incorporatedas above in solutions or dispersions of these materials.

This. invention is chiefly concerned with soluble, solid derivatives ofnatural rubber hydrocarbons, such as I-levea rubber, which has theempirical formula (CEHBM, which. derivatives have less unsaturation thanHevea rubber when it contains an equivalent quantity of one or moreadded elements, such for example as chlorine, sulphur; selenium, andtellurium, chemically combined therewith. It has also been found,however, that synthetic rubbers, such as polymerized butadiene bodiesand even a polychl'oroprene (neoprene) and mixtures of these materialswith natural rubber, and others, form derivatives when heated with theacidic or acid forming rubber conversion reagents in substanti'ally' thesame manner as set forth above. Fliese derivatives also have the samecarbon and hydrogen ratio" as their parent synthetic rubber and haveless unsaturation than the syntheti'c rubb'er when it contains an equalamount of any added elements combined therewith. They are especiallydesirable for bonding the synthetic rubbers to metal. The bond producedby these soluble. derivatives is also strengthened and improved whensulphur or selenium is incorporated in their solutions. 7

' The. rubber derivatives susceptible of improvement according to thepresent invention by incorporating: vulcanizing agents in theirdispersions or solutionsare members of the group consisting of; isomersof rubber and isomers of incompletely saturated addition products ofrubber. They are not completely saturated, but they have less chemicalunsaturationxthan the rubber or the simple addition. products of therubber with which they are isomeric. Thus, for example, although thederivatives contemplated in the present invention may have the empiricalformula of 'the usual incompletely saturated halogen, hydrohalogen,sulphur or selenium addition products of rubber, they are distinguishedfrom such simple (substantially unpolymerized) addition products of thesame chemical composition by having less chemical unsaturation.

It is desirable that the derivatives have some unsaturated double bondsin order that vulcanizing agents may more readily affect bridges betweenmolecules during the curing operation and a higher heat resistance maybe obtained in the composite article produced. The isomers of theaddition products of rubber, and particularly the isomers of sulphur andselenium additionv products of rubber, have been found to be moredesirable for the purposes of the present invention than the rubberisomers.

When it is desired to compound an adhesive for use either for adheringrubber to metal or adhering a synthetic rubber, such as neoprene(polychloroprene), to metal, it is desirable to incorporate. asubstantial amount of a solvent of .relatively low volatility, such askerosene, or a plasticizing agent, such s light mineral oil, in thesolutions of the adhesive, as it has been found that this considerablyimproves the adhesion of synthetic rubbers to metal, and also forms agood bond between rubber and metal.

While the vulcanizing agents, sulphur and selenium, have been mainlyemphasized throughout the specification, it is to be understood thattellurium, and even vulcanizing types of accelerators, such astetramethylthiuram disulphide, etc., may be used, either for thecomposition for the adhesive or for the paint.

In the appended claims, the term rubber unless specifically qualified isintended to include synthetic rubbers as well as natural rubber, and theterm rubber derivative is intended to include derivatives of natural andthe synthetic rubbers, which form soluble rubber derivatives whentreated with the conversion reagents, heated and masticated as abovedescribed, such synthetic rubbers being generally those vulcanizing orcombining chemically with sulphur. v

It is to be understood. that variations and modifications of theprocedures herein shown and described for purposes of illustration maybe made without departing from the spirit of the invention.

What I claim is;

1. In a method of producing adhesives of a type having desirableproperties for bonding rubber to metal, the steps which comprise formingasolution of cyclized rubber derivative having the same carbon tohydrogen ratio as the rubber from which it was derived and having lesschemical unsaturation than the rubber and any incompletely saturatedrubber addition products of the same percentage composition as saidderivative, and incorporating 5% to 50% of sulphur based on saidderivative throughout said dissolved derivative, said derivative beingthe heat reaction product of a mixture of rubber and an agent capable ofcyclizing rubber, the greater portion of said sulphur being distributedthrough said derivative after said derivative was dissolved.

2. A rubber-to-metal adhesive having as itsprincipal.organic'constituent a solution of an organic solid, whichconsists of an unsaturated isomer of an incompletely saturated rubberaddition product having the same carbon to hydrogen ratio as rubber andhaving less chemical unsaturation than both rubber and rubber additionproducts of the same percentage composition with which it is an isomer,said solution containing about 5% to about 50% of sulphur, based on theweight of the dissolved organic constituent.

3. In a method for improving the heat resistance of an adhesive film ofa cyclized unsaturated rubber derivative having the same carbon tohydrogen ratio as the rubber from which it was derived and having lesschemical unsaturation than the rubber or any unsaturated rubber additionproducts of the same percentage composition with which it is isomeric,the step which comprises mixing at least 5% sulphur with said derivativeprior to forming said film, a substantial proportion of said sulphurbeing incorporated intimately through said derivative after forming thesolution thereof.

4. An adhesive for bonding rubber and'compounds thereof to a rigidmaterial comprising a solution of a rubber derivative prepared byreacting with heat in a form having thin section a mixture of rubber, asalt of a strong acid and water, said derivative being characterized byhaving the same carbon to hydrogen ratio as rubber, by having lessplasticity than does rubber at elevated temperatures of the order of 100C., and

by having less chemical unsaturation than rubber and simple unsaturatedrubber addition products with which it is an isomer, said adhesivecontaining about 5% to about 50% of sulphur based on said derivative.

5. An adhesive for bonding a rubber and compounds thereof to a rigidmaterial, comprising a solution of a rubber derivative having the samecarbon-to-hydrogen ratio as rubber and having less chemical unsaturationthan any rubber addition product of the same percentage composition,which solution contains about 5% to about 50% of sulphur, based on theamount of the solid rubber derivative in said solution.

6. An adhesive for bonding a rubber and compounds thereof to a rigidmaterial, comprising a solution of a rubber derivative having the samecarbon-to-hydrogen ratio as the rubber from which it was derived andhaving less chemical unsaturation than any rubber addition product I ofthe same percentage composition, which solution contains about 5% toabout 50% of elements selected from the group consisting of sulphur,selenium, and tellurium, said percentage being based n the amount of thesolid rubber derivative in said solution.

7. An adhesive for bonding a rubber and compounds thereof to a rigidmaterial, comprising a solution of a rubber derivative containing up toabout 3% of combined sulphur and having the same carbon-to-hydrogenratio as rubber and less chemical unsaturation than a simple rubberaddition product of the same percentage composition, said solution beingfurther characterized by having about 5% to about 50% of sulfurchemically uncombined with said rubber derivative.

8. The adhesive of claim 6 also containing a vulcanization acceleratorof a type having an anti-plasticizing effect when it is incorporated insolid unvulcanized rubber.

9. The adhesive of claim 6 also containing 2,4- diamino-diphenylamine.

10. The adhesive of claim 6 also containing a member of the groupconsisting of accelerators and anti-oxidants for rubber, whichaccelerators and anti-oxidants are characterized by having ananti-plasticizing effect on uncured solid rubber mixes when incorporatedtherein,

11. An adhesive for .bonding a rubber and compounds thereof to a rigidmaterial, comprising a solution of a rubber derivative having the samecarbon-to-hydrogen ratio as rubber and having less chemical unsaturationthan any rubber addition product of the same percentage composition,said solution being further characterized by containing selenium in anamount up to 15% of said derivative and about 5% to about of sulphur,which sulphur is based on said derivative and is not chemically combinedtherewith.

12. The adhesive of claim 6 containing sulphur in amounts of about 15%to about 50% of the weight of the rubber derivative.

13. An adhesive for bonding rubber and compounds thereof to a rigidmaterial comprising a solution of a rubber derivative prepared byreacting with heat in a form having thin section a mixture of rubber, asalt of a strong acid and water, said derivative being characterized byhaving the same carbon-to-hydrogen ratio as rubber, by having lessplasticity than does rubber at ele-. vated temperatures of the order ofC., and by having less chemical unsaturation than rubber and simpleunsaturated rubber addition products with which it is an isomer, saidadhesive containing about 15% to about 50% of sulphur chemicallyuncombined with said rubber derivative, said amount of sulphur beingbased on the quantity of the solid rubber derivative in said adhesive.

14. In a method of producing an adhesive fo bonding a rubber orcompounds thereof to a rigid material, which adhesive has as aningredient a rubber conversion product characterized by having lessplasticity than has crude rubber at temperatures of the order of 100 C.,by having less chemical unsaturation than rubber or rubber additionproducts with which it is an isomer,

by having the same carbon-to-hydrogen ratio as rubber, and by being theheat reaction product of a masticated mixture of solid rubber and arubber conversion reagent comprising a salt of a strong acid and water,the steps which comprise incorporating sulphur into a solution of saidrubber derivative, said sulphur being present in the amounts of about 5%to about 50% of the weight of said derivative, the major portion thereofbeing incorporated with said derivative after form,- ing a solutionthereof in a suitable solvent.

15. The method of claim 14 in which selenium is incorporated with saidrubber derivative prior to forming a solution thereof.

THOMAS RAYMOND GRIFFI'II-I.

